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2.7.  Details of Edit Commands
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<a name="Details of Edit Commands">
<h3>
2.7.  Details of Edit Commands
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<a name="Undo and Redo">
<h4>
2.7.1.  Undo and Redo
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<p>
When the user selects <tt>Undo</tt> from the <tt>Edit</tt> menu, the system
undoes the effect of the most recently confirmed updating command.
<p>
When the user selects <tt>Redo</tt> from the <tt>Edit</tt> menu, the system undoes the effect of a previously executed <tt>Undo</tt> command.

<a name="text editing">
<a name="Cut, Copy, and Paste">
<h4>
2.7.2.  Cut, Copy, and Paste
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<p>
<a name="clipboard">
Operating systems typically provide a "clipboard" area through which cut and
paste editing commands operate.
</a>
This clipboard holds values that are cut, copied, and pasted in tools such as
the Schedule.  Hence, the <tt>Schedule</tt> <tt>Cut</tt>, <tt>Copy</tt>, and
<tt>Paste</tt> commands operate through such a clipboard.
<p>
To execute the <tt>Cut</tt> or <tt>Copy</tt> command, the user must first
select a segment of text in a text box.  Text selection is performed using
click and drag with the mouse, or by other environment-specific means such as
double or triple clicking in a text box.
<p>
After text selection, when the user selects the <tt>Cut</tt> command from the
<tt>Edit</tt> menu, the system removes the selected text from the edit box and
copies the text into the clipboard.  When the user selects the <tt>Copy</tt>
command, the selected text is copied to the clipboard, but is not removed from
the display in which it is selected and the text remains selected.  A
particular segment of selected text is <em>unselected</em> by selecting another
text segment or by single-clicking the mouse anywhere in the Scheduling display.
<p>
<a name="text cutting restrictions">
The <tt>Cut</tt> command can only be executed in the context of a display where
the text boxes are editable, i.e., where the user may type in the text boxes.
</a>
In contrast to <tt>Cut</tt>, the <tt>Copy</tt> command can be executed in any
dialog in which text boxes appear, including read-only text boxes.
<p>
To execute the <tt>Paste</tt> command, the user must first execute a
<tt>Cut</tt> or <tt>Copy</tt> and then place the typing cursor within some
editable text box.  After these steps, when the user selects the <tt>Paste</tt>
command from the <tt>Edit</tt> menu, the text stored in the clipboard is
inserted at the point of the typing cursor, as if it had been entered by the
user from the keyboard.  Pasted text appears in normal font, i.e., it is not
highlighted as selected text.
<p>
If the user attempts to execute a <tt>Cut</tt> or <tt>Copy</tt> command without
first selecting text, the commands have no effect.  If the user attempts to
execute a <tt>Paste</tt> command without having executed either a <tt>Cut</tt>
or <tt>Copy</tt>, the <tt>Paste</tt> command has no effect.  The <tt>Cut</tt>,
<tt>Copy</tt>, and <tt>Paste</tt> commands operate only on plain text strings
within a single displayed text box.  In particular, the commands do
<em>not</em> apply to a scheduled item.


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